Matthew Poole and continuators on Psalms 104:19

19 He appointeth the moon for seasons ; the sun knoweth his going down .

To measure and distinguish the times, both Months, and, amongst many Nations, Years also; as also the Seasons of divers natural events, as of the ebbing and flowing of the Waters, and of the humours in mans Body; and other Seasons for sacred and civil affairs, which were commonly regulated by the Moon, not onely amongst the Jews, but among Heathens also. See on Gen. 1. 14.

To wit, the time and place in which he is to set every day of the Year, which, though varied from day to day, yet he so regularly and exactly observes, as if he had the understanding of a Man or Angel to guide him in obeying the Laws of his Creator. See Iob 38. 12. What is here expressed concerning his setting is necessarily supposed concerning his rising also; but he mentions onely his setting, as most agreeable to the context, because that did usher in the rising of the Moon, of which he now spake, and the entrance of the night, of which he speaks in the next words.